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THE  CORROSION  OF  METALS  IN  DILUTE 
ORGANIC  ACIDS 

BY 

JEAN  CHARLOTTE  SHEPHERD 
B.  A.  University  of  Montana 
1919 


THESIS 

Submitted  in  Partial  Fulfillment  of  the  Requirements  for  the 

Degree  of 

MASTER  OF  SCIENCE 

IN 

CHEMISTRY 

IN 

THE  GRADUATE  SCHOOL 

OF  THE 

UNIVERSITY  OF  ILLINOIS 


1921 


■ 


. 


YbSA 

SVV 

UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


i q?i 


I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 
SUPERVISION  BY  JEAN  CHARLOTTE  STfKPtraTTT) 


ENTITLED  TM_0QRH03I0IL^^iEgi3X3  III  DILUTE  ORO-Al TP)  AJYTTjS 


BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF Master  of  Science 


Recommendation  concurred  in* 


Committee 

on 

Final  Examination* 


""Required  for  doctor’s  degree  but  not  for  master’s 


/ 


0 C ^ A\ 


AGJfflOVflEDGMEH  T 

±he  autnor  takes  this  opportunity  to  express  her  appreciation 
and  most  sincere  thanks  to  Doctor  J.  H.  Reedy  for  his  valuable 
help  and  direction  so  kindly  and  freely  given  in  this  investigation. 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/corrosionofmetalOOshep 


TABLE  OF  COIT TENTS 

I INTRODUCTION 

I I EXPERIMEN TAL  PA  RT 

(a) A  Discussion  of  Methods 

( b ) Apparatus 

( c ) Legend 

III  DISCUSSION 

( 1 ) Gene  ral 

(2)  Propionic  acid 

(3)  Tartaric  acid 

(4)  Citric  acid 

( 5 ) Alanine 

(6)  effect  of  Previous  Treatment  of  Metal 


Page 

1 

3 

3 

5 

7 

7 

16 

25 

25 

38 

39 


IV  SUMMARY 

V BIBLIOGRAPHY 


40 


1- 


THE  CORROSION  OP  LIE TALS  BY  DILUTE  ORGANIC  ACIDS 
I.  INTRODUCTION 

This  p ro bl era  was  suggested  by  the  corrosion  of  milk  containers 
used  in  the  Dairy  Department  of  the  University.  The  acid  concen- 
tration in  milk  varies  from  O.OOl  H to  0.1  E,  the  stronger  acid  being 
found  in  sour  milk.  These  aoids  consist  of  a mixture  of  amino, 
ny  roxy,  and  unsubstituted  mono=,  di-,  and  tricarboxylic  acids, 
in  the  following  experiments  an  attempt  has  been  made  to  compare 
tne  rate  of  corrosion  of  various  metals  in  each  type  of  acid. 

According  to  the  electrolytic  theory  of  corrosion  advanced 
by  Whitney1,  iilden^,  and  others,  every  metal  has  a certain  solution 
tension  which  differs  for  different  metals  and  depends  also  on  the 
pnysical  state  of  the  metal.  If  we  immerse  any  metal  in  water, 
it  te.ids  to  go  into  solution  to  form  positive  ions  leaving  the 
metal  negatively  charged.  Unless  we  remove  this  negative  charge 
from  the  metal,  the  electrostatic  force  between  the  metal  and  the 

ions  soon  equals  the  solution  tension  of  the  metal  and  solution 

will  cease. 

If  we  have  a crystalline  metal,  different  parts  of  the  crystals 
Will  nave  different  solution  tensions  and  we  will  have  small  cells 
formed  between  different  parts  of  the  metallic  surface.  In  this 
oase,  hydrogen  will  be  liberated  at  the  surface  of  the  metal,  but 
the  h.  II.  I\  is  so  small  that  the  hydrogen  cannot  escape  as  a gas . 

It  polarizes  the  cell,  and,  unless  it  is  removed  by  some  means, 
corrosion  will  cease.  Dissolved  oxygen  tends  to  combine  directly 
with  the  hydrogen  and  therefore,  if  we  have  oxygen  present,  the 
natal  will  corrode  until  the  supply  of  oxygen  is  used  up. 

Ii  we  nave  an  impure  metal,  v,e  have  two  substances  of  different 


* 


t 


. . ' 


. 


2- 

aolution  tensions  and  we  will  have  a corrosion  cell  established  as 
before.  The  E.  Ivl.  F.  in  this  case  is  somewhat  larger  and  the 
hydrogen  liberated  may  pass  off  as  a gas.  All  or  part  of  the 

hydrogen  however,  may  combine  with  dissolved  oxygen. 

7 

Bengough,  in  his  work  on  the  corrosion  of  brass,  has  defined 
two  types  of  corrosion,  "complete",  in  which  all  of  the  substances 
present  are  removed  in  the  proportions  inwhich  they  occur  in  the 
sample,  and  "selective",  in  which  corrosion  takes  place  at  the 
expense  of  the  constituent  having  the  highest  solution  tension. 
Complete  corrosion  depends  entirely  upon  dissolved  oxygen  and  the 
amount  of  metal  dissolved  is  directly  proportional  to  the  amount 
of  oxygen  consumed.  "Dezincification described  by  Bengough, 
in  the  case  of  brass  in  sea  water,  is  an  example  of  selective 
corrosion  and  may  be  accompanied  by  the  evolution  of  hydrogen. 

It  is  well  known  that  strains  brought  about  by  the  bending  and 
twisting  of  a metal  increase  the  rate  of  corrosion.  Also,  sharp 

edges  and  points  on  a surface  corrode  more  rapidly.  This  compli- 

cates the  problem  of  comparing  the  rates  of  corrosion  of  different 
samples  because  of  surface  differences  between  the  pieces  of  metal. 
Temperature  and  the  presence  of  even  minute  traces  of  impurities 
cause  marked  differences  in  the  rate  of  corrosion. 


, 


, 


, 


c 

3- 


II.  EXPERIMENTAL  PART 

(a)  Disoussion  of  Methods.-  The  usual  method  of  measuring 
the  rate  of  corrosion  is  to  immerse  the  weighed  sample  in  the 
solvent  for  a given  length  of  time,  usually  weeks  or  even  months, 
then  clean  hy  careful  washing  and  weigh  again.  In  strong  solution* 
and  with  large  samples,  the  difference  is  easily  weighable , and 
the  loss  on  cleaning  is  negligible.  However,  with  dilute  solu- 
tions after  only  a few  days  time,  the  loss  in  weight  is  a matter 
of  tenths  of  a milligram  at  most  and  the  loss  on  cleaning  becomes  a 
larger  factor  in  the  accuracy  of  measurement. 

-ilso  , in  tne  above  method,  the  rate  of  corrosion  is  assumed  to 
be  a straight  line  function.  There  is  no  evidence  to  support 
this  assumption  because  the  composition  of  the  solution  is  contin- 
ually changing. and  many  reactions  of  this  type  exhibit  the  phenome- 
non of  an  induction  period. 

On  the  other  hand,  corrosion  of  pure  metals  or  metals  contain- 
ing only  traces  of  impurities  by  dilute  solutions,  is  always  accom- 
panied by  the  absorption  of  oxygen.  This,  then  seems  to  offer  a 
means  of  measuring  a very  small  loss  in  the  sample  with  a higii 
aegree  or  accuracy.  By  using  an  air  tight  container  connected 
to  a manometer,  small  changes  in  the  volume  of  gas  can  be  calculated 

from  daily  readings  and  a true  measure  of  rate  of  corrosion  obtain- 
ed . 

(b)  Apparatus .-  A diagram  of  the  manometer  cell  used  is  given 
lx:  figure  1.  It  was  found  necessary  to  use  ground  glass  stoppers, 
as  rubber  stoppers  were  not  air  tight  under  the  conditions  of  the 
experiment,  even  when  resurfaced  with  sealing  wax  and  shellac.  A 
few  of  the  stoppers  used  did  appear  to  hold  a vacuum,  but  as  a rule 


vt 

. 

, 

* 


. 


F;«I 


5- 


They  oould  not  be  depended  upon.  It  may  be  that  under  a vacuum, 
air  leaks  slowly  through  the  pores  of  the  rubber.  A spark  was 
passed  between  the  platinum  points  AA , at  intervals  during  the 
course  of  the  experiment  to  test  for  the  presence  of  hydrogen. 

The  mercury  in  the  manometer  showed  a tendency  to  distil  over 
on  to  the  metal.  This  was  especially  noticeable  in  the  case  of 
copper,  because  the  presence  of  the  mercury  on  the  surface  of  the 
sopper  seemed  to  inhibit  corrosion.  A thin  layer  of  ilujol  was 
put  on  top  of  the  mercury  to  prevent  this  distillation.  ! 

The  strips  of  metal  had  a uniform  surface  area  of  17.7  sq.  cm. 
The  dimensions  were  not  exactly  the  same  in  each  case,  because  the 
metals  could  not  be  obtained  in  sheets  of  the  same  thickness.  The 
strips  were  all  very  thin,  however,  in  comparison  to  the  length  and 
width.  The  volume  of  the  solution  was  the  same  in  each  case  (50  cc ) 
and  as  the  manometer  cells  we  re  of  practically  the  same  volume, 
the  volume  of  oxygen  present  in  each  case  was  very  nearly  the  same. 

The  manometer  cells  , when  filled  were  placed-  on  a shaking 
machine  having  a gentle  horizontal  motion  in  order  to  keep  the 
solution  saturated  with  oxygen. 

Due  to  the  complicated  nature  of  the  apparatus  and  its  conse- 
quent limited  supply,  all  the  experiments  could  not  be  run  at  the 
same  time  under  exactly  the  same  conditions.  In  this  respect,  the 
results  are  not  strictly  comparable.  In  order  to  make  daily  read- 
ings independent  of  volume  changes  due  to  temperature  and  atmos- 
pheric pressure,  a blank  was  run  using  a manometer  cell  of  the  same 
size  as  the  others  containing  50  cc.  of  water. 

(c)  legend.-  In  all  of  the  following  ta'oles,  the  time  is 
given  in  days,  Dx  represents  the  daily  difference  in  level  of  raer- 


6- 


cury  for  the  first  sample,  Dg , the  difference  in  the  secoiid  sample, 
and  C the  difference  for  the  manometer  cell  run  as  a blank.  The 
number  of  units  equivalent  to  one  cc . of  oxygen  in  each  case  is 
given  at  the  bottom  of  the  column.  For  G in  all  cases  1 cc.  Or, 
is  equivalent  to  10.4.  The  results  are  expressed  in  cc . of  oxygen 
absorbed . 

Each  of  the  following  graphs  represents  a series  of  experiments 
run  at  the  same  time,  under  the  same  conditions. 


7- 


III.  DISGUSSIOH  OF  RESULTS. 

(a)  General.-  In  looking  over  the  data,  there  are  two  points 
thatstrike  one  rather  forcibly.  In  the  first  place,  none  of  the 
curves  are  straight  lines.  In  other  words,  if  a sample  loses 

0.5  grams  in  5 days  , we  are  not  justified  in  assuming  that  it  lost 
0.1  gram  the  first  day.  In  most  cases  the  reaction  was  ran  id  lor 
the  first  day  or  two,  gradually  falling  off  to  zero.  ( Platesl3 ,14) 

In  Plates  3,4,  however,  we  have  evidence  of  a marked  period  of 
induction. 

In  the  second  place,  there  is  a wide  variation  in  the  results 
obtained  in  the  two  samples  run  as  checks.  In  general,  the  two 
curves  obtained  are  of  the  same  shape,  but  it  is  impossible  to 
obtain  the  same  absolute  values.  The  main  source  of  this  dis- 
crepancy is  the  difference  in  condition  of  the  two  metallic  sur- 
faces. Ko  amount  of  polishing  can  bring  them  to  exactly  the  same 

state.  While  the  values  obtained  are  not  absolute,  they  are  good 

enough  to  enable  us  to  draw  certain  conclusions,  concerning  the 
action  of  an  acid  on  varioiis  metals. 

(b)  Propionic  Acid  (Table  I,  II,  III,  IT;  Plates  I,  II,  III,  IV I 
The  rates  of  corrosion  of  copper,  tin,  zinc,  and  aluminum  are  what 

we  would  expect  from  considerations  given  in  the  first  part  of  this 
paper.  In  general,  the  rate  is  dependent  on  the  solution  tension 
of  the  metal  and  the  hydrogen  ion  concentration  of  the  solution. 

The  data  given  indicate  that  copper  corrodes  more  rapidly  than 
tin,  but  in  tne  case  of  copper,  the  corrosion  product  was  soluble 
while  in  the  case  of  tin,  a white  precipitate  settle^  pn  the  surface 
oi  tne  metal.  This  may  account  for  the  apparent  contradiction  to 
the  general  rule.  The  precipitate  in  normal  acid  was  much  heavier 


. 

« 


* 


- 


- 

• 

t r r 

C t 

f 

. 


r 


* 


Copper  in  Propionic  Acid 


N 


Days 

C 

D 

cc . 0 

0 

0.00 

0.58 

0.000 

1 

0.13 

1.69 

0.049 

3 

-1.05 

3.21 

0.245 

5 

- 1.85 

4.37 

0.389 

7 

-£.26 

5.91 

0.515 

9 

-1.93 

7.65 

1 cc=crl8. 
11/ 10 

0.579 

0 

0.00 

1.0C 

0.000 

1 

0.15 

2.38 

0.092 

3 

-1.05 

3.00 

0.265 

5 

-1.85 

4.21 

0.419 

7 

-2.26 

5.40 

0.551 

9 

-1.93 

7.23 

1 cc^xL3.2 
11  / 100 

0.669 

0 

0.00 

0.60 

0.000 

1 

0.13 

0.81 

0.009 

3 

-1.05 

0.20 

0.071 

5 

-1.85 

- 0.09 

0.143 

7 

-2.26 

0.18 

0.188 

9 

-1.93 

0.39 

1 cc<^15 

K/1000 

0.171 

0 

0.00 

C.36 

0.000 

1 

0.13 

1.25 

0.054 

3 

-1.05 

0.30 

0.094 

5 

-1.85 

- 0.49 

0.104 

7 

- 2.26 

-1.02 

0.104 

9 

- 1.95 

- 0.54 
1 ccci3.2 

0.117 

9- 


xin  in  Propionic  Acid 
E 


Days 

G 

D 

0 

0.00 

0.60 

1 

0.15 

1.65 

n 

-1.05 

1.76 

5 

- 1.85 

1 . 65 

7 

- 2.26 

2.75 

9 

- 1.95 

5.50 

1 ccc^15. 6 

N/10 

0 

0.00 

0.92 

1 

0.15 

2.15 

5 

- 1.04 

2.90 

5 

- 1.85 

5.52 

7 

- 2.26 

5.99 

9 

- 1.95 

5.20 

1 cc=0=-18.0 

H/100 

0 

0.00 

0.50 

1 

0.15 

0.95 

5 

- 1.05 

0.50 

5 

- 1.85 

- 0.46 

7 

- 2.26 

-0.72 

9 

-1.95 

-0.50 
1 0CO18.4 

H/1000 

0 

0.00 

0.71 

1 

0.15 

1.08 

5 

-1.05 

0.21 

5 

-1.84 

r-  0.67 

7 

-2.26 

- 0.87 

9 

-1.95 

- 0.28 
1 cc  =c=l 5 . 0 

cc . 02 

0.000 

0.064 

0.186 

0.254 

0.574 

0.584 


0.000 
0.080 
0 . 247 
0.547 
0.445 
0.501 


0.000 

0.012 

0.087 

0.126 

0.150 

0.142 


0.0C0 

0.008 

0.071 

0.102 

0.1.25 

0.125 


Aluminum  in  Prop  ionic  Acid. 
H 


Days 

C 

D 

oc . 0 

0 

0.00 

0.49 

0.000 

1 

0.13 

1.20 

0.055 

3 

-1.05 

2.00 

0.241 

5 

-1.85 

2.79 

0.385 

7 

-2.26 

4.33 

0.580 

9 

-1.93 

6.07 

0.615 

1 cc=0=10.6 

11/10 

0 

0.00 

0.44 

0.000 

1 

0.13 

1.63 

0 • 062 

3 

- 1.05 

2.77 

0.238 

5 

- 1.85 

3 . 59 

0.258 

7 

- 2.26 

4.61 

0.476 

9 

- 1.93 

6.69 

0.558 

1 CCCrl6.ffi 

11/100 

0 

0.00 

0.42 

0.000 

1 

0.13 

2.14 

0.086 

3 

- 1.05 

3.45 

0.266 

5 

-1.85 

3.84 

0.378 

7 

- 2. £6 

4.67 

0.454 

9 

-1.93 

5.90 

0.500 

1 GCr0rl8 

H/1000 

0 

0.00 

0.46 

0 . OOC 

1 

0.13 

1.03 

0.025 

3 

-1.05 

0.39 

0.092 

5 

-1.85 

-0.22 

0.161 

7 

— 2.26 

0.06 

0.189 

9 

- 1.93 

0.20 

C .167 

1 ccrC=15 


11- 


Zinc  in  Propionic  Acid 
H/lOO 


Pays 

C 

D 

cc . 0 

0 

0.00 

0.82 

0.000 

1 

0.13 

2.14 

0.059 

3 

-1.05 

2.90 

0.212 

5 

-1.85 

2.70 

0.281 

7 

-2.26 

2.69 

0.319 

9 

- 1.93 

3.55 

0.334 

1 CC<Jrl8.4 

N/1000 

0 

0 . 00 

0.53 

0.000 

1 

0.13 

2.06 

0.082 

3 

- 1.05 

3.55 

C.264 

5 

- 1.85 

4.19 

0.380 

7 

- 2.26 

5.14 

0.473 

9 

- 1.93 

6.89 

0.548 

1 CCr^lS 


P I-/=f  ~r  E: 


Of\  ys 


D&ys 


P*  vs 


pL/=f  T£T 


ys 


16- 


than  in  0.1  N and  it  did  not  appear  at  all  in  0.01  N acid  and 
0.001  N acid  solutions.  Copper  in  normal  and  0.1  N solutions  re- 
mained bright,  but  in  0.01  E and  0.001  E solutions  it  was  covered 
with  a dark  coating  which,  looked  like  copper  oxide. 

Samples  of  zinc  were  tried  in  Formal  and  0.1  N solutions. 

They  were  corroded  very  rapidly,  and  so  much  hydrogen  was  evolved 
in  the  reaction  that  it  pushed  the  mercury  out  of  the  manometer  in 
the  course  of  a few  minutes.  No  measurements  of  the  rate  of 
corrosion  of  these  samples  could  be  made  by  means  at  hand. 

The  data  given  for  aluminum  indicates  that  by  using  manometer 
cells  the  rate  of  corrosion  in  even  .01  normal  and  .001  E solutions 
can  be  measured  fairly  accurately.  This  is  in  contradiction  to 
Seligman  and  Williams^,  who  said  that  no  trustworthy  data  could  be 
obtained  on  the  corrosion  of  aluminum  in  dilute  acids. 

(c)  Tartaric  acid  (Tables  V,  VI,  VII,  VIII;  Plates  Y,  VI,  VII, 
VIII).—  There  is  some  indication  that  copper  forms  an  unionized 
complex  with  the  OH  groups  in  tartaric  acid4.  Then,  from  the 
lavv  oi  mass  action,  we  would  expect  copper  to  corrode  more  rapidly 
in  tartaric  than  in  propionic.  The  results  obtained  in  these 
experiments  indicate  tnat  the  opposite  is  true.  The  temperature 
in  the  propionic  acid  experiments  was  several  degrees  higher,  but 
even  this  is  not  enough  to  account  for  the  difference.  Copper  in 
normal  tartaric  actually  shows  an  expansion  of  the  gas.  There  was 
no  contraction  on  sparking  for  several  minutes  and  the  author  can 
offer  no  explanation  for  this  behavior. 

Ine  tartaric  acid  solutions  in  which  tin  was  immersed,  remain- 
ed clear  in  all  cases,  and  the  metal  darkened  appreciably,  indicat- 
ing a deposit  of  some  sort  on  its  surface.  A.  C.  Chapman5  has  done 


' 


■ 


t 

♦ 

. 


17- 


Days 

0 

1 

2 

3 

4 

5 

6 
7 
9 


0 

1 

2 

3 

4 
9 

10 


0 

1 

2 

3 

4 

5 

6 
7 
9 


0 

1 

2 

3 

4 
9 

10 


C 

-0.10 

0.10 

0.22 

0.10 

- 0.46 

- 0.10 

- 0.24 

0.66 

0.25 


- 0.89 

- 0.83 
0.80 
1.05 
0.24 
1.29 
0.75 


- 0.10 
0.10 
0.22 
0.10 

- 0.46 

- 0.10 

- 0.24 

0.66 

0.25 


- 0.89 

- 0.83 
0.80 
1.05 
0.24 
1.29 
0.75 


Aluminium 

*1 

- 0.40 

- 0.03 
0.36 
0.34 
0.39 
1.15 
1.13 
2.46 
2.74 

1 cc  *3=18.5 


0.65 
0.63 
2.64 
3 . 20 
2.36 
4.62 
4.00 

1 CG:Crl6.8 


— 0.23 
0.47 
1.34 
1.62 

1.40 
2.28 
2.32 
3.96 

4.40 

1 cc  =0=18 


0.53 

1.25 

2.66 

3.20 

2.35 

3.56 

3.03 

l 3 C o 


in  Tartaric  Acid 
E 


oc . 02 

D2 

0.000 

- 0.40 

0.001 

- 0.06 

0 . 010 

0.58 

0.020 

0.75 

0.075 

0.63 

0.086 

1.47 

0.093 

1.39 

0.081 

2.75 

0.136 

2.79 

1 ccO=18 

D/10 

0.000 

0.28 

0.000 

0.11 

- 0.039 

0.11 

- 0.029 

1.16 

- C.005 

-0.05 

0.034 

4.30 

0.050 

2.70 

1 cc=£>18 

K/100 

0.000 

- 0.35 

0.019 

0.44 

0.054 

1.31 

0.084 

1.52 

0.125 

1.45 

C.140 

2.25 

0.155 

2.27 

0.160 

3.89 

0.224 

4.32 

1 cc=c=13.2 

K/1000 


0.000 

0.37 

0.034 

1.01 

- 0.044 

2.76 

- 0.038 

3.05 

- 0.007 

2.02 

-r-  0.041 

3.37 

-0.017 

2.71 

1 CC=OlQ 

GG 

0 

0 

0 

0 

0 

0 

0 

0 

0 


0 

- 0 
- 0 
- 0 
- 0 

c 

- 0 


0 

0 

0 

0 

0 

0 

0 

0 

0 


0. 

0. 

- 0. 
- 0. 
- 0. 
- 0. 
- 0. 


.000 
.000 
. 023 

.045 

.082 

.094 

.113 

.1005 

.143 


.000 

.015 

.1706 

.1398 

.1192 

.0144 

023 


000 

029 

095 

123 

171 

195 

215 

247 

320 


000 

029 

033 

041 

019 

062 

031 


18- 

Zinc  in  Tartaric  Acid 


H/100 

Days 

C 

D1 

cc . Og 

*2 

cc . 0. 

0 

- 0.1 

0.000 

0.000 

0.000 

0.000 

1 

0.1 

1.13 

0.049 

0.30 

0.096 

2 

0.22 

2.35 

0.108 

1.46 

0.052 

3 

0.10 

2.48 

0.127 

1.60 

0.071 

4 

- 0.46 

2.45 

0.180 

1.50 

0.012 

5 

- 0.10 

3.51 

0.208 

2.23 

0.126 

6 

- 0.24 

3.05 

0.195 

2.30 

0.144 

7 

0.66 

4.38 

0.187 

3.70 

0.137 

9 

0.25 

4.38 

0.226 

3.79 

0.181 

1 cc^>16.8 

N/ 1000 

1 000=17 .6 

0 

- 0.89 

0.55 

0.000 

0.53 

0.000 

1 

- 0.83 

1.30 

0.028 

1.35 

C.038 

2 

0.80 

3.15 

-0.014 

3.56 

0.002 

3 

1.05 

3.60 

-0.004 

5.38 

0.076 

4 

0.24 

3.27 

0.0399 

5.55 

0.164 

9 

1.29 

10.80 

0.374 

13.80 

0.506 

10 

0.75 

11.12 

0.446 

13.20 

0.525 

1CC017.6 

1 ccO-18 .4 

Tin  in  Tartaric  Acid 
E/1000 

19- 

Days 

C 

®i 

CC  . Og 

B2 

cc . 02 

0 

— 0.89 

0.4 

0.000 

0.53 

0.000 

i 1 

-0.83 

0.6 

0.00704 

0.9 

0.0187 

2 

0.80 

2.32 

0.0416 

2.55 

- 0.0277 

3 

1.05 

2.7 

0.0409 

2.9 

- 0.0277 

4 

0.24 

1.68 

0.0229 

1.83 

- 0.0218 

9 

1.29 

2.91 

0 . 0421 

3.22 

- 0.0276 

10 

0.75 

2.3 

1 cc=C=15 

B/100 

0.0315 

1 

2.32 

cc=o=15 

- 0.0219 

0 

-0.1 

- 0.15 

0.0000 

•0.17 

0.0000 

1 

0.1 

0.2 

0.C0021 

0.3 

0.0052 

2 

0.22 

5.57 

0.0287 

0.33 

- 0.0043 

3 

0.1 

7.05 

0.0381 

0.17 

0.00302 

4 

- 0.46 

7.72 

0.445 

- 

0.2 

0.02186 

6 

- 0.1 

9.15 

0.517 

— 

0.13 

0.0221 

7 

- 0.24 

9.3 

0.537 

— 

0.2- 

0.0114 

8 

0.66 

10.75 

0.505 

1.0 

0.0064 

10 

0.25 

10.93 
i cc=c=ie 

H/10 

0.581 

1 

0.59 

CC  =0:18 

0.0063 

0 

- 0.89 

0.52 

0.0000 

0.45 

o.ooco 

1 

- 0.83 

2.49 

0.108 

2.29 

0.132 

2 

0.80 

4.48 

0.038 

4.28 

0.127 

3 

1.05 

5.88 

0.112 

5.57 

0.191 

4 

0.24 

5.32 

0.159 

5.21 

0.251 

9 

1.29 

9.75 

0.305 

9.92 

0.510 

10 

0.75 

9.25 

1 ccoig 

■K 

0.328 

1 

9.40 

cc=C>13 . 2 

0.519 

0 

- 0.1 

- 0.4 

0.000 

— 

0.3 

0.000 

1 

0.1 

1.19 

0.0549 

1.16 

0.0596 

2 

0.22 

2.32 

0.190 

3.48 

0.209 

3 

0.1 

3.9 

0.244 

4.23 

0.273 

4 

— 0.46 

3.93 

0.305 

4.47 

0.352 

6 

- 0.1 

4.59 

0.310 

5.23 

0.362 

7 

- 0.24 

4.26 

0.310 

5.12 

0.367 

8 

0.66 

4.97 

0.266 

6.24 

0.358 

10 

0.23 

4.83 

1 c c =C»1 5 

0.293 

1 

5.7 

cc  =015 

0 .363 

Copper  in  Tartaric  Acid 


H 


Days 

C 

D1 

cc . 02 

^2 

CC  . Or 

0 

- 0.10 

-0.50 

0.000 

-0.35 

0.000 

1 

0.10 

0.00 

- 0.0186 

0.35 

0.019 

2 

0.22 

0.28 

0.028 

0.50 

0.016 

3 

0.10 

- 0.22 

0.002 

0.16 

0.009 

4 

- 0.46 

- 1.02 

- 0.003 

- 0.92 

0.009 

5 

- 0.10 

- 1.50 

- 0.076 

- 1.27 

- 0.048 

6 

_ 0.24 

- 2.03 

- 0.102 

- 1.85 

-0.070 

7 

0.66 

- 0.95 

- 0.107 

0.07 

- 0.049 

9 

0.25 

- 1.75 

- 0.128 

- 0.05 

- 0.017 

10 

- 0.89 

- 3.71 

- 0.167 

- 4.44 

- 0.150 

11 

- 0.83 

- 3.32 

- 0.144 

0.00 

- 0.089 

12 

0.80 

-1.65 

- 0.173 

0.00 

_ 0.070 

13 

1.05 

-1.35 

-0.174 

- 0.24 

-0.007 

15 

0.24 

-2.45 

-0.180 

- 0.90 

— 0.063 

20 

1.29 

-1.32 

-0.195 

- 2.08 

-0.230 

21 

0.75 

-2.32 

-0.220 

-1.52 

_ 0.147 

1 cc=C=-13 

.2 

1 oc=018 

li/100 

0 

- 0.10 

” 0.26 

o.oco 

- 0.23 

0.000 

1 

0.10 

0.84 

0.041 

0.90 

0.070 

2 

0.22 

2.61 

0.126 

2.41 

0.148 

3 

0.10 

3.17 

0.167 

2.94 

0.199 

4 

- 0.46 

2.6 

0.190 

2.98 

0.256 

5 

- 0.10 

4.77 

0.274 

3.59 

0.267 

6 

-0.24 

4.54 

0.274 

3.39 

0.275 

7 

0.66 

5.59 

0.242 

5.80 

0.356 

9 

0.25 

5.47 

0.278 

5.70 

0.414 

10 

- 0.89 

5.504 

0.386 

4.70 

0.424 

11 

-0.83 

4.70 

0.349 

4.94 

0.447 

12 

0.80 

6.38 

0.274 

6.57 

0.398 

13 

1.05 

6.68 

0.268 

7.16 

0.408 

15 

0.24 

6.03 

0.308 

6.20 

0.474 

20 

1.29 

5.47 

0.176 

7.65 

0.432 

21 

0.75 

6.88 

0.306 

6.98 

0.434 

1 cc^>18.4  1 cc^C=13.6 


Pl  ft  T E 


Dh  rs 


* 


. 


S'A  h/CJ 


D n y_5 


25- 


sorae  work  on  the  corrosion  of  tin  in  tartaric  acid.  He  analyzed 
the  corrosion  product  and  found  that  it  consisted  of  a mixture  of 
oxides  of  tin.  This  would  be  expected  from  the  fact  that  tin 
compounds  as  a rule  hydrolyze  easily. 

Aluminum  corrodes  appreciably  in  normal  and  .01  K tartaric 
acid  and  does  not  corrode  at  all  in  0.1  and  .001  IT.  Something 
analogous  to  this  has  been  described  by  Heyn  and  Bauer^  who  worked 
with  iron  and  steel  in  various  salt  solutions.  They  found  that  in 
many  cases  (all  that  they  recorded)  the  corrosive  action  does  not 
vary  with  the  concentration  of  solution  in  any  regular  manner. 

The  data  on  aluminum  also  contradicts  somewhat  the  statement 
of  G.  H.  Bailey  that  the  corrosion  of  aluminum  in  tartaric  acid 
is  negligible. 

Zinc  corrodes  more  rapidly  in  .001  II  tartaric  than  in  .01  H. 

As  in  the  case  of  propionic  acid,  zinc  in  normal  and  0.1  F solutions 
reacts  to  give  hydrogen. 

(d)  Citric  acid ( Tables  IX,  X,  XI,  XII;  Plates  IX,  X,  XI,  XII).- 
xhe  results  obtained  writh  citric  acid  are  closely  analogous  to  those 
obtained  with  propionic  except  in  the  case  of  aluminum.  Aluminum 
in  the  more  dilute  acids  corrodes  more  rapidly  than  in  the  more 
concentrated. 

(e)  Alanine  (Tables  XIII,  XIV,  XV,  XVI;  Plates  XIII,  XIV,  XV, 
aVI) .-  Prom  the  fact  that  alanine  contains  both  an  amino  group 
and  a carboxyl  group,  we  would  not  expect  it  to  behave  like  an 
ordinary  acid.  Guch  an  assumption  is  fully  justified  by  the  re- 
sults obtained , especially  with  copper  and  zinc. 


Copper  is  corroded  very  rapidly  in  alanine,  and  a very  dark 
blue  solution  results.  This  leads  to  the  conclusion  that  copper 


t 


. 


Copper  in  Citric  Acid 


E 


Days 

C 

*2 

cc . Og 

D2 

cc  . 0 

0 

0.50 

0.05 

0.000 

- 0.05 

0.000 

1 

0.46 

0.70 

0.040 

0.84 

0.063 

£ 

0.33 

1.06 

0.072 

1.35 

0.115 

3 

-0.15 

1.10 

0.121 

1.46 

0.169 

4 

0.14 

1.18 

0.097 

1.48 

0.143 

5 

0.12 

0.95 

0.087 

1.24 

0.127 

7 

- 0.12 

0.95 

0.109 

1.25 

0.149 

9 

0.05 

0.98 
1 cc*>18 

0.096 

1.13 

1 cc:C&3.2 

0.125 

E/ 10 


0 

1.09 

0.26 

0.000 

0.25 

0.000 

1 

0.40 

0.33 

0.070 

0.22 

0.059 

2 

“ 0.12 

0.10 

0.107 

0.00 

0.092 

4 

-0.C7 

0.20 

0.108 

- 0.10 

0.080 

8 

0.00 

0.68 

0.0532 

- C.24 

0.062 

10 

- 0.52 

0.78 

0.096 

-0.24 

- C .050 

13 

- 0.59 

0.25 
1 00=018 

0.133 

- 3.08 
1 ccoG.3.2 

- 0.096 

E/100 


0 

0.50 

0.29 

0.000 

0.24 

0.000 

1 

0.46 

0.54 

0.017 

0.52 

0.019 

2 

0.33 

0.55 

0.032 

0.63 

0.032 

3 

-0.15 

0.92 

0.096 

1.10 

0.109 

4 

0.14 

1.00 

0.073 

1.20 

0.087 

5 

0.12 

1.02 

0.076 

1.21 

0.089 

7 

- 0.12 

1.02 

0.099 

1.22 

0.113 

9 

0.05 

1.09 

0.091 

1.43 

0.108 

1 ccol8.4 

1 ccol8.4 

E/lOOO 


0 

1.09 

0.20 

0.000 

0.27 

0.000 

1 

0.40 

-0.41 

0.078 

-0.27 

0.025 

2 

-0.12 

-0.99 

0.050 

-0.72 

0.041 

4 

-0.07 

-0.79 

0.096 

-0.56 

0.049 

8 

0.00 

0.66 

0.129 

-0.52 

' 0.045 

10 

-0.52 

-1.27 

0.073 

-1.09 

0.052 

13 

-0.59 

-1.28 

0.079 

-1.09 

0.056 

1 CC=Crl8 

1 cc  =o=15 

27- 


Aluminum  in  Citric  Acid 


B 


Lays 

C 

D1 

cc.  Og 

»2 

0 

0.50 

-0.15 

0.000 

-0.23 

1 

0.46 

. 0.2 

0.025 

- 0.50 

2 

0.33 

0.05 

0.027 

0.44 

3 

-0.15 

-0.1 

0.065 

- 0.51 

4 

0.14 

-0.09 

0.038 

- 0.40 

5 

0.12 

-0.1 

0.039 

0.40 

7 

-0.12 

0.09 

0.073 

- 0.28 

9 

0.05 

0.41 

0.076 

0.23 

1 ccsO.6. 

8 

1 ccol7 

E/10 

0 

1.09 

0.15 

0.000 

0.19 

1 

0.4 

C .45 

0.084 

-0.44 

2 

-0.12 

-0.77 

0.062 

— C .72 

4 

-0.07 

-0.25 

0.104 

-0.07 

8 

0.00 

0.39 

0.119 

0.46 

10 

-0.52 

0.07 

0.142 

0.16 

13 

-0.59 

0.38 

0.130 

0.49 

1 cc«Q.6. 

8 

1 c co-1 7 

H/100 

0 

0.50 

0.45 

0.000 

0.16 

1 

0.46 

0.48 

0.005 

0.30 

2 

0.33 

0.70 

0.035 

0.49 

3 

-0.15 

0.88 

0.086 

0.56 

4 

0.14 

1.13 

0.071 

0.82 

5 

0.12 

1.25 

0.080 

0.86 

7 

-0.12 

1.45 

0.115 

1.13 

9 

0.05 

1.90 

0.124 

1.60 

1 CC018 

1 ccol8 

E/1000 

0 

1.09 

0.10 

0.000 

0.15 

1 

0.40 

— 0.20 

0.0717 

0.29 

2 

-0.12 

—0.68 

0.075 

-0.73 

4 

-0.07 

-0.35 

0.087 

- 0.45 

8 

0.00 

— 0.13 

0.092 

- 0.21 

10 

— 0.52 

- 0.74 

0.109 

-0.73 

13 

-0.59 

— 0.75 

0.115 

-0.67 

1 cc-=c=18 

.4 

1 CC=C=l8 

cc . Og 

0.000 
— 0.073 
0.053 
0.046 
0.051 
0.050 
0.033 
0.086 


0.000 

0.080 

0.065 

0.097 

0.120 

0.153 

0.177 


0 . 000 
0.0116 
0.035 
0.085 
0.071 
0.075 
0.113 
0.123 


0.000 

0.076 

0.071 

0.081 

0.087 

0.109 

0.119 


28- 


Tin  in 

Citric  Acid 

T.T 

Days 

C 

D1 

Li 

cc . 02 

D2 

0 

0.50 

0.33 

0.000 

0.05 

1 

0.46 

1.88 

0.1173 

2.15 

2 

0.33 

2.58 

0.1827 

3.45 

3 

-0.15 

2.94 

0.2545 

4.41 

4 

0.14 

3.33 

0.2537 

5.12 

5 

-0.12 

5.42 

0.2640 

5.43 

7 

0.12 

4.22 

0.3453 

5.95 

9 

0.05 

5.00 

u.3864 

6.62 

1 cc^13.6 

1 

cc^c=18 

0 

1.09 

0.52 

0.000 

0.40 

1 

0.4 

1.93 

0.265 

1.24 

2 

-0.12 

2.15 

0.234 

2.39 

4 

-0.07 

6.08 

0.519 

5.19 

8 

0.00 

8.73 

0.709 

7.49 

10 

-0.52 

8.75 

0.759 

7.58 

13 

-0.59 

9.15 

0.796 

8.08 

1 cc  **13 . 6 

1 cc=c=18 

K/100 


0 

0.50 

0.03 

0.000 

0.54 

1 

0.46 

3.20 

0.197 

2.35 

2 

0.33 

4.56 

0.300 

3.52 

5 

-0.15 

5.3 

0.395 

4.15 

4 

0.14 

5.58 

0.386 

4.81 

5 

0.12 

6.05 

0.420 

5.07 

7 

-0.12 

6.55 

0.477 

5.54 

9 

0.05 

7.39 

0.515 

7.37 

1 cc=c=15 

1 cc^18 

H/ 1000 

0 

1.09 

0.2 

0.000 

0.29 

1 

0.40 

-0.2 

0.0396 

-0.35 

2 

-0.12 

•0.33 

0.0809 

-0.94 

4 

— 0.07 

0.52 

0.133 

-0.65 

8 

0.00 

0.69 

0.137 

0.59 

10 

-0.52 

0.06 

0.145 

-1.13 

13 

-0.59 

0.16 

0.149 

— 1*09 

1 00=0*15 

1 cc-**15 

cc . Og 

C.000 

0.121 

0.203 

0.324 

0.316 

0.336 

0.435 

0.407 


0.000 

0.112 

0.226 

0.377 

0.498 

0.552 

0.587 


0.000 
0 .1022 
0.1761 
0.2561 
C .2660 
0.2837 
0.3318 
0.4140 


0.000 

0.227 

0.232 

0.343 

0.4729 

0.57C 


* 


Zinc  ii 


Days 

C 

% 

0 

0.5 

0.00 

1 

0.46 

-0.70 

S 

0.33 

1.30 

3 

-0.15 

0.47 

4 

-0.14 

0.70 

5 

0.1E 

0.80 

7 

-0.1S 

1.17 

9 

0.05 

1.91 

1 cc=e=15 


i Citric  Acid 
E/100 


cc.  02 

DS 

cc . l 

0.000 

0.00 

0.000 

0.043 

-0.E8 

0.017 

0.1C3 

0.19 

0.031 

0.094 

1.04 

0.016 

0.07E 

0.90 

0.10E 

0.091 

0.8E 

0.098 

0.114 

-0.3 

0.08S 

0.171 

0.77 

0.10E 

1 cc^LS.E 


0 

1 

E 

4 

8 

10 

13 


1.09 
0.4 
-0.1E 
-0.07 
0.00 
-0.5S 
— C .59 


E/1000 


0.3 

0.000 

0.08 

0.054 

-0.C7 

0.096 

0.14 

0.097 

0.54 

0.118 

-0.1S 

0.133 

-0.11 

0.139 

1 cc=£>18.4 

0.41 

0.000 

• 0.09 

0.048 

-0.S9 

0.077 

0.10 

0.081 

C.55 

0.113 

— 0.  S3 

0.119 

- 0.04 

0.136 

1 cc=O18.0 

P l n ~r  e TK. 


Dft  YJ 


S' A t=/  Cl 


P L-  /-?  -r  B XL 


f 


Dft  ys 


D n ys 


Zinc  in  Alanine 


K/10 


Days 

0 

D1 

cc . 0£ 

*2 

CC  . Or 

0 

0.7 

1.21 

0.000 

2 

0.4 

4.95 

0.218 

4 

-0.4 

6.77 

0.403 

6 

-0.4 

9.15 

0.525 

8 

0.6 

11.80 

0.573 

10 

1.17 

16.15 

0.744 

1 cc^18 

N/100 

0 

0.99 

0.24 

0.000 

0.36 

0.000 

1 

-0.2 

2.95 

0.318 

3.3 

0.279 

2 

0.1 

4.52 

C.409 

5.29 

0.358 

4 

0.7 

7.00 

0 • 635 

8.69 

0.491 

6 

0.82 

9.45 

0.714 

9.66 

0*534 

7 

0.82 

11.56 

0.878 

10.15 

0.506 

9 

0.78 

11.54 

0.876 

11.22 

0.242 

1 00*0.3.2 

o 

• 

CO 

4 

o 

o 

H 

IT/ 1000 


0 

0.& 

2.6 

0.000 

1.02 

C.000 

2 

0.4 

6 .36 

0.238 

5.3 

0.338 

4 

-0.4 

7.97 

0.403 

7.17 

0.447 

6 

-0.4 

10.0 

0.516 

9.19 

0.568 

8 

0.6 

12.56 

0.563 

10.82 

0.554 

10 

1.17 

14.2 

0.687 

1 ccx:18 

1 cc*18.0 

Tin  in  Alanine 


36- 


E 


lays 

C 

D1 

cc  . 02 

»2 

cc . 0( 

0 

0.99 

0.05 

0.000 

*-0.4 

0.000 

1 

-0.2 

1.09 

0.191 

0.74 

0.153 

2 

0.1 

1.52 

0.193 

0.86 

0.130 

4 

0.7 

2.41 

0.201 

2.51 

0.165 

6 

0.82 

2.93 

0.228 

1.89 

0.138 

7 

0.82 

3.74 

0.288 

2.05 

0.137 

9 

0.78 

3.55 

loc^>13 . 6 

0.279 

2.21 

1 CC=Crl8 

0.141 

E/10 


0 

0.7 

1.31 

0.000 

1.54 

0.000 

2 

0.4 

1.4 

0.034 

1.6 

0.034 

4 

-0.4 

0.48 

0.060 

0.78 

0.048 

6 

-0.4 

0.54 

0.063 

0.089 

0.057 

8 

0.6 

1.89 

0.041 

2.23 

0.062 

10 

1.17 

2.6 

0.026 

2.98 

0.064 

1 ccol8 

1 cc**13.2 

E/100 


0 

0.99 

0.15 

0.000 

0.56 

0.000 

1 

-0.2 

0.2 

0.117 

1.55 

0.181 

2 

0.1 

1.47 

0.159 

1.90 

0.175 

4 

0.7 

2.18 

0.140 

2.56 

0.161 

6 

0.82 

2.36 

0.139 

2.72 

0.160 

7 

0.82 

2.37 

0.159 

2.80 

0.165 

9 

0.78 

3.21 

0.190 

2.75 

0.165 

1 cc=e=18 

1 CCsOO.5.0 

E/1000 

0 

0.7 

2.7 

0.000 

1.99 

0.000 

2 

0.4 

3.08 

0.053 

2.11 

0.036 

4 

-0.4 

2.32 

0.084 

1.26 

0.056 

6 

-0.4 

2.40 

0.089 

1.38 

C.066 

8 

0.6 

3.22 

0.037 

2.69 

0.057 

10 

1.17 

4.41 

0.049 

3.31 

0.042 

1 ccoQ.8 . 

4 

1 c c.=c*15.0 

Aluminum  in  Alanine 


Days 

0 

1 

2 

4 

6 

7 

9 


0 

2 

4 

6 

8 

10 


0 

1 

2 

4 

6 

7 

9 


0 

2 

4 

6 

8 

10 


TS 


G 

*>1 

oc.  Cg 

»2 

CG.Og 

0.99 

0.12 

0.000 

0.15 

0.000 

-0.2 

1.07 

0.171 

0.83 

0.0381 

0.1 

1 » 52 

0.169 

0.95 

0.0544 

0.7 

1.46 

0.170 

1.35 

0.0097 

0.82 

3.33 

0. 209 

1.70 

0.0279 

0.82 

3.86 

0.234 

2.21 

0.0570 

0.78 

4.04 

0.255 

1.89 

0.0427 

1 

cc^iLG  .8 

1 

cc*c0l7 . 6 

H/lO 

0.7 

1.46 

0.000 

1.20 

0.000 

0.4 

1.99 

0.060 

2.1 

0.079 

-0.4 

2.19 

0.149 

2.83 

0.198 

-0.4 

4.16 

0.266 

0.00 

0.037 

0.6 

0.08 

1.17 

( exploded ) 

( exploded ) 

1 

cc*s£L6 .8 

1 

cc=&17.6 

E/100 

0.99 

0.42 

O.OCO 

0.52 

0.000 

-0.2 

1.39 

0.168 

2.28 

0.215 

0.1 

1.82 

0.164 

2.85 

0.212 

0.7 

2.76 

0.155 

4.91 

0.266 

0.82 

3.26 

0.170 

6.48 

0.342 

0.82 

3.40 

0.177 

7.19 

0.379 

0.78 

3.74 

0.201 

7.99 

0.425 

1 

ce^l8.4 

1 

cc*JiL8 .4 

D/1000 


0.7 

0.71 

0.000 

0.4 

0.86 

0.037 

-0.4 

0.03 

0.069 

-0.4 

0.04 

0.069 

0.6 

1.36 

0.045 

1.17 

2.12 

0.032 

1 ee*>18.4 

2 .24  0.000 

3.8  0.012 

0.72  0.018 

( exploded) 


cc  .4 


1 


Copper  in  Alanine 

N 


35- 


Lays 

0 

1 

2 

4 

6 

7 

9 


0 

2 

4 

6 

8 

10 


0 

1 

2 

4 

6 

7 

9 


0 

2 

4 

6 

8 

10 


c 

D1 

GG  . Og 

®2 

CG  . Og 

0.99 

0.15 

0.000 

0.2 

0.000 

— 0.2 

2.43 

0.2415 

-0.4 

0.827 

0.1 

4.10 

0.305 

0.39 

0.728 

0.7 

6.6 

0.387 

0.6 

0.496 

0.82 

8.38 

0.473 

0.58 

0.370 

0.82 

9.2 

0.518 

0.33 

0.235 

0.78 

10.2 

0.579 

0.89 

0.578 

1 

cc=£t18. 

0 

1 

oc4>18 .4 

IT/10 

0.7 

1.31 

0.000 

1.58 

0.000 

0.4 

4.54 

0.266 

5.33 

0.314 

-0.4 

5.49 

0.413 

7.58 

0.438 

-0.4 

6.38 

0.477 

9.49 

0.544 

0.6 

9.26 

0.595 

11.49 

0.569 

1.17 

10.96 

0.664 

14.18 

0.654 

1 

cc^»13 . 6 

1 

C 0=018 . 0 

1/100 

0.99 

2.28 

0.000 

0.35 

0.000 

-0.2 

2.2 

0.109 

0.13 

0.1 

3.13 

0.142 

0.1 

0.666 

0.7 

4.73 

0.191 

0.1 

0.084 

0.82 

5.1 

0.205 

0.05 

0.064 

0.82 

5.09 

0.204 

0.07 

0.049 

0.78 

5.1 

0.209 

0.1 

0.012 

1 

cc=ol5 

1 

cc*c=13.2 

IT/ 1000 

0.7 

0.68 

0.000 

0.43 

0.000 

0.4 

1.25 

0.072 

0.23 

0.015 

—0.4 

0.68 

0.106 

— 0.43 

0.0484 

-0.4 

0.68 

0.106 

-0.27 

0.0591 

0.6 

1.95 

0.106 

1.07 

0.0435 

1.17 

2.73 

0.112 

2.79 

0.0392 

1 

cc=csl3. 

2 

1 

g£  ^<>15 .0 

. 


PL-  Fl  ~TE  Z 


S' a y a 


D /=?  YS 


[Zl  a JJZ' 


D f=\  vs 


rA  ^ cj 


58- 

forms  some  sort  of  a complex  with  the  amine,  which  is  analogous  to 

. + + 

the  Cu(hH3 )4  ion  formed  when  BH4OH  is  added  to  a copper  salt 
solution . 

Zinc  also  forms  complex  ions  with  NHg , and  from  its  rapid 
corrosion  rate  in  alanine,  such  a complex  is  probably  formed  in 
this  case  with  the  amine. 

(f)  The  Effect  of  Previous  Treatment  of  the  Metal.-  The  re- 
sults with  aluminum  in  alanine  were  rather  unexpected.  Three 
pieces  of  aluminum,  the  three  that  gave  such  large  amounts  of  hy- 
drogen.had  been  used  several  times  before-,  being  carefully  cleaned 
and  polished  between  successive  experiments.  The  other  piece  in 
.001  B acid  was  new.  This  brings  out  rather  forcibly  that  previous 
treatment  of  a metal  has  much  to  do  with  speed  of  corrosion.  In 
making  the  sheet  of  aluminum,  the  impurities  present  were  probably 
covered  up  by  a layer  of  pure  aluminum.  On  continued  treatment 
in  acids  this  outer  layer  was  dissolved  off,  exposing  the  impurities 

and  giving  opportunity  for  "selective"  corrosion.  All  of  these 
three  pieces  were  pitted. 

xxiis  problem  is  by  no  means  finished.  The  author  hopes  to  be 
able  to  clear  up  many  points  that  have  been  touched  on  in  this- 

paper,  by  later  research,  and  to  enlarge  the  scope  of  the  work 
somewhat . 


. 


« 


, 

• 

- 

. 


. 


. 


- 


* 


39- 


SUMMABY 

I.  Hate  of  corrosion  is  not  a straight  line  function  of  the 
time,  and  cannot  be  accurately  determined  by  measuring  the  amount 
of  material  removed  after  a given  period  of  time,  and  assuming  a 
uniform  rate  over  the  entire  period.  The  reasons  suggested  are 
(a)  the  changing  composition  of  the  solution,  and  fb)  the  tendency 
for  an  inductive  period  at  the  beginning  of  the  reaction. 


II.  Two  strips  of  metal,  of  the  same  size  cut  from  the  same 
sheet  and  treated  in  the  same  way  do  not  corrode  at  the  same  rate 
because  of  surface  differences  which  cannot  be  eliminated. 

III.  There  was  no  hydrogen  evolved  in  most  of  the  reactions 

studied . 


IV.  The  corrosion  of  pure  metals  in  dilute  organic  acids  is 
accompanied  by  t.ie  absorption  of  oxygen  and  the  amount  of  metal  re 
moved  is  proportional  to  the  amount  of  oxygen  consumed.  In  ether 

words,  it  corresponds  to  the  "complete”  corrosion  described  by 
Bengough. 


/.  The  rate  of  corrosion  of  a metal  in  an  unsubstituted  acid 
is  dependent  upon  the  "solution  tension"  of  the  metal  and  the 
hydrogen  ion  concentration  of  the  solution. 

VI.  The  effect  of  presence  of  OH  groups  as  exemplified  by 
tartaric  acid  cannot  be  explained  in  the  light  of  the  present  theory 
and  more  v/ork  is  necessary  to  explain  the  results. 

>11.  Ine  presence  of  an  amino  group  in  the  molecule  leads 
to  tne  formation  oi  complexes  analogous  to  complexes  formed  by 

copper  ana  zinc  ions  with  EH3,  and  therefore  these  metals  corrode 


more  rapidly  in  this  type  of  acid. 

/III.  The  rate  of  corrosion  of  a metal  by  acids 
ly  on  the  previous  treatment  of  the  metal. 


depends  large 


. 

. 


* 

. 

. 

• 

• 

, 

. 

* 

n>  ■ 


, 

* 


. 


BIBLIOGRAPHY 


1.  Whitney ,-Joum.  Am.  Ghem.  Soc.  25,-394. 

2.  Tilden,-Joum.  Am.  Ghem.  Soc.  93,-1356. 

3.  Seligman  and  Williams ,-Jourg.  Soo.  Ghem.  Ind . 36,-409. 

4.  Holleman ,-5th  edition,  page  241. 

5.  A.  G.  Chapman,- J.  Chem.  T.  775-103. 

6.  Heyn  and  Bauer , -"Tiber  den  Angriff  des  Eisens  durch  Wasser 

und  WSsserige  LSsungenV  Mitteilungen  aus  dem  Kdniglichen 
Materialprtifungsamt , Berlin,-  1910,  28,-62,  1908,  26,-2. 

7.  Bengough,-J.  Inst.  Met.  10,-50. 


